Solvent extraction with increased polar hydrocarbon purity

ABSTRACT

A solvent extraction process for effecting the separation of polar hydrocarbons from a mixture thereof with non-polar hydrocarbons. A polar hydrocarbon stream, containing solvent, is passed through two separation zones having a zone of turbulence therebetween, to recover polar hydrocarbons substantially free from solvent. The process is especially adaptable for utilization in the recovery of substantially pure aromatic hydrocarbons from a mixture thereof with non-aromatic hydrocarbons.

Sates Patent Van 'lassell Feb. 4, 1975 [54] SOLVENT EXTRACTION WITH3,492,222 1/1970 vsii Tassel] 208/321 INCREASED POLAR HYDROCARBON3,714,033 1/1973 Somekh et al. 208/321 PURITY Primary Examiner-HerbertLevine [75] Inventor: Harry M. Van Tassell, Arlington Attorney, Agent orFirm JameS Hoatson, J

Hmghts, Robert w. Erickson; William H. Page, ll [73] Assignee: UniversalOil Products Company,

Des Plaines, Ill. [57] ABSTRACT [22] Filed; 23 7 A solvent extractionprocess for effecting the separation of polar hydrocarbons from amixture thereof [21] PP bio-14182699 with non-polar hydrocarbons. Apolar hydrocarbon stream, containing solvent, is passed through two sep-[52] US. Cl 208/321, 208/325, 208/333 aration Zones having a Zone ofturbulence therebe- [51] Int. Cl C10g 21/28 tween to recover Polarhydrocarbons Substantially [58] Field of Search 208/321 free fromSolvent The process is especially adaptable for utilization in therecovery of substantially pure ar- [56] References Cited omatichydrocarbons from a mixture thereof with nonaromatic hydrocarbons.

3.173.966 3/1965 Jones et a1. 208/321 11 Claims, 1 Drawing FigureStripper Receiver .Sepam/ion Zone A/Sa/vetrf S/ripper ExgzzcJ/on Exlrac//30 3 Race/yer Entrainment Sepnrufor SOLVENT EXTRACTION WITH INCREASEDPOLAR HYDROCARBON PURITY APPLICABILITY OF INVENTION The invention hereindescribed is intended for utilization in the separation, and ultimaterecovery of polar hydrocarbons from a mixture thereof with non-polarhydrocarbons, which separation is effected through the use of a solventcharacteristically selective for adsorbing polar hydrocarbons. Morespecifically, my invention is directed toward the separation andrecovery of aromatic hydrocarbons from various mixtures thereof withnon-aromatic hydrocarbons, which process utilizes two-stage separationwith intermediate turbulence for the purpose of recovering an aromaticconcentrate substantially free from solvent.

In the present specification, as well as the appended claims, the use ofthe terms polar and non-polar" is intended to distinguish betweenvarious classes of hydrocarbons wherein one particular type is morepolar while another is less polar. For example, in the extraction ofaromatics from a mixture thereof with naphthenes and/or paraffins, thelatter are considered nonpolar" with respect to the former which arepolar. The process utilizes a solvent which may be indefinitely recycledwithin the system, separates the desired hydrocarbon productssubstantially in their entirety from the feed stocks charged to theprocess and yields the desired polar hydrocarbons in high purity, beingsubstantially free from both solvent and non-polar hydrocarbons. Thatis, the polar hydrocarbon purity is greater than 99.5% by weight, andthe product contains less than about 500 ppm. of solvent.

The present invention is particularly concerned with an improvement in atype of separation process wherein a mixture of various classes ofhydrocarbons is introduced into a solvent extraction zone, beingcountercurrently contacted therein with a solvent selective for theadsorption or aromatic hydrocarbons. A rafflnate phase, comprisingsubstantially all of the nonaromatic hydrocarbons in the feed stock (atleast about 90.0% by weight), is removed from an end portion of theextraction zone, and an extract phase comprising the aromatic componentsis removed from the other end portion of the extraction zone, with thearomatic solute being recovered therefrom in a solvent stripping zonethrough the utilization of steam. The present invention is particularlydirected to the further removal of solvent from the aromatic solute, inorder to recover an aromatic concentrate virtually free from solvent.

My invention is applicable for use with any hydrocarbon feed stockhaving a sufficiently high aromatic concentration to justify therecovery thereof i.e., at least about 25.0% by volume. The overallcarbon number range of suitable charge stocks is from about 6 to about10. These charge stocks will generally include, in addition to C C and C-aromatics, non-aromatics which can predominate in C and C -paraffinsand naphthenes. Exemplary of various sources of suitable charge stocksare the depentanized effluent from a naphtha catalytic reforming unit,coke-oven by-products, wash oils, hydrotreated pyrolysis naphtha, etc.

My inventive concept involves a unique procedure for the removal ofsolvent from hydrocarbon fractions separated by way of extractivedistillation, or combinations of extraction and extractive distillation.In a solvent extraction process, the term solvent stripping is LIIemployed to connote the technique wherein a polar hydrocarbon-richsolvent stream iscontacted with steam to provide a solvent concentratesubstantially free from hydrocarbons, a vaporous stream comprisingsteam, solvent and hydrocarbons, and a polar hydrocarbon concentratehaving a reduced solvent content and containing steam. The presenttechnique is advantageous in that it affords additional removal ofsolvent from the polar hydrocarbon concentrate emanating from thesolvent stripping zone. A distinct improvement is afforded thoseprocesses wherein steam is generated, for utilization in the solventstripping zone, from various water streams separated within the physicalconfines of the solvent extraction process. The present technique hasmany advantages over currently-practiced prior art procedures. Principalamong these is an increase in the purity of the desired polarhydrocarbon product accompanied by enhanced solvent recovery within theprocess. Other advantages are hereinafter discussed, and will becomeevident to those possessing the requisite skill in the appropriate art.

PRIOR ART It must be recognized that the prior art is prolific with awide spectrum of solvent extraction processes utilized for effecting theseparation of polar and non-polar hydrocarbonaceous mixtures. No attemptwill be made herein to exhaustively delineate the appropriate publishedliterature; it will suffice to note several examples which appear to betypical of prior art practices and procedures, and to which the presentinvention is most suitably applicable. Solvent extraction processes aregenerally specifically directed to the recovery of aromatic hydrocarbonsfrom a mixture thereof with nonaromatic hydrocarbons. Furthermore, thegreater majority of such processes indicate a distinct preference for awater-soluble solvent containing an oxygenated organic compound. Areview of the relevant prior art indicates that the prevalent solvent iseither a sulfolanetype organic compound, or an alltylene glycol, thelatter preferably being a polyalkylene glycol. While most prior artprocesses are intended for utilization with either of these organicsolvents, specific techniques do exist which are peculiar either to one,or the other.

U.S. Pat. No. 3,173,966 (Cl. 260-674) incorporates rectification of richsolvent side-cut vapors, withdrawn from the solvent stripping zone inorder to recover substantially solvent-free water for subsequentutilization within the process. In U.S. Pat. No. 3,396,101 (Cl.208-313), a mixture of charge stock and lean solvent is introduced intoa stripping column, from which a non-aromatic overhead stream iswithdrawn and introduced into an extraction zone. The resulting richsolvent is passed from the reaction zone to the stripping column as asecond feed stream thereto.

U.S. Pat. No. 3,436,435 (Cl. 260-674) involves the utilization of anentrainment separator into which a side-cut aromatic stream, from thesolvent stripping zone, is introduced. The process as illustratedfurther incorporates an integrated system for handling the variouswater-containing streams. Still another variation, in the-integratedprocess flow of a solvent extraction unit, is that found in U.S. Pat.No. 3,723,256 (Cl. 203-43). Initially, the aromatic hydrocarbon feed isintroduced into a distillation column from which a light fraction and aheavier bottoms fraction is recovered. The former is passed into anextractive distillation tower, while the latter is introduced into aliquid extraction unit. The extract from the liquid extraction unit isstripped of non-aromatic hydrocarbons to produce a nonaromatics freefraction and a non-aromatics containing fraction. The aromaticsrecovered in admixture with the solvent, from the extractivedistillation tower, are passed to a recovery section in admixture withthe aromatic-containing fraction from the stripping zone. The overheadstream from the extractive distillation column, in admixture with thenon-aromatics from the stripping zone, is passed to the bottom sectionof the solvent extraction zone, to function therein as a reflux stream.

A perusal of the foregoing illustrations of prior art processes willindicate that the improvements afforded thereby result primarily from avariety of modifications with respect to internal flow of variousprocess streams. That is, a common characteristic of the multitude ofsolvent extraction processes is the utilization of at least a solventextraction zone and a solvent stripping zone. For a given solventextraction unit, designed to process a given quantity of mixedhydrocarbon feed stock, these two vessels, and the required manifoldingand miscellaneous vessels appurtenant thereto, are the principal factorsdetermining both erection and operating cost. It may be said, therefore,that economically attractive innovations relate to various techniquesutilized with respect to the internal flow of various process streams.The resulting enhancement generally stems from improved and/orsimplified unit operations, lower operating utility cost, improvedproduct purity, increased solvent recovery within the process, loweroverall initial capital investment, etc. The technique encompassed by myinventive concept is applicable to the foregoing described processes,and affords the indicated advantages therein.

OBJECTS AND EMBODIMENTS A principal object of my invention is directedtowards increased purity of the polar hydrocarbon product streamrecovered from a solvent extraction process. A corollary objectiveresides in increased solvent recovery.

Specifically, my invention affords significant economic advantages whenintegrated into currentlypracticed solvent extraction systems for theseparation and recovery of polar hydrocarbons from mixtures thereof withnon-polar hydrocarbons.

Therefore, in one embodiment, my inventive concept encompasses a processfor the solvent extraction of polar hydrocarbons from mixture thereofwith nonpolar hydrocarbons, in which process the method of recoveringsaid polar hydrocarbons, substantially free from solvent, comprises thesteps of: (a) contacting a polar hydrocarbon-rich solvent stream withsteam to provide (i) a first solvent concentrate substantially free frompolar hydrocarbons, (ii) a vaporous stream containing steam, solvent andhydrocarbons and (iii) a vaporous first polar hydrocarbon concentrate ofreduced solvent content and containing steam; (b) separating said firstpolar hdyrocarbon concentrate, in a first separation zone, to provide(i) a second solvent-rich stream and (ii) a vaporous second polarhydrocarbon concentrate of reduced solvent content, and containingsteam; (c passing said second polar hydrocarbon concentrate through azone of turbulence at a temperature of about 60F. to about l80F.; and,(d) separating the resulting turbulent polar hydrocarbon concentrate, ina second separation zone, to provide (i) a water concentrate, containingsolvent, and (ii) a third polar hydrocarbon concentrate substantiallyfree from solvent.

These, as well as other objects and embodiments of my invention, willbecome evident from the following detailed description thereof. Briefly,however, with respect to such other embodiments, these involve operatingconditions, particular solvents, in-process separations and streamflows, etc. For example. preferred solvents include alkylene glycols,polyalkylene glycols and sulfolane-type organic compounds. In a specificembodiment, directed toward the integration of my inventive concept intoa solvent process for the selective separation and recovery of aromatichydrocarbons from a mixture thereof with non-aromatic hydrocarbons, saidaromatic hydrocarbons, substantially free from nonaromatic hydrocarbonsand solvent, are recovered by a method which comprises the steps of a)contacting said mixture with a water-soluble solvent, selective for theadsorption of aromatic hydrocarbons, in a solvent extraction zone, toprovide (i) a solvent-rich first extract stream, and (ii) a solvent-leanfirst raffinate stream; (b) contacting said first raffinate stream witha first water stream to provide (i') a second raffinate streamsubstantially free from solvent and concentrated in non-aromatichydrocarbons, and (ii) a second water stream containing solvent and aminor quantity of hydrocarbons; (c) admixing said second water streamwith a substantially pure, first aromatic stream and separating theresulting mixture to provide (i) a second aromatic stream, containingnon-aromatic hydrocarbons, and (ii) a third water stream substantiallyfree from non-aromatic hydrocarbons; (d) generating steam from saidthird water stream and contacting said first extract stream therewith ina solvent stripping zone; (e) recovering, from said stripping zone, i) avaporous stream containing steam, hydrocarbons and solvent, (ii) a firstsolvent-rich stream, and (iii) a vaporous second extract stream,concentrated in aromatic hydrocarbons, and containing solvent and steam;(f) separating said second extract stream, in a first separation zone,to provide (i) a second solvent-rich stream, and (ii) a third extractstream of reduced solvent content and containing steam; g) passing saidthird extract stream through a zone of turbulence at a temperature inthe range of 60F. to about F.; and, i h) separating the resultingturbulent third extract stream, in a second separation zone to provide afourth water concentrate containing solvent, and to recover aromatichydrocarbons substantially free from solvent.

SUMMARY OF INVENTION Although applicable to a multitude of hydrocarbonmixtures, further discussion will be limited to the separation andrecovery of aromatic hydrocarbons from a mixture thereof with paraffinsand/or naphthenes. lnitially, the mixture of hydrocarbons is contacted.with a water-soluble, oxygen-containing solvent particularly selectivefor the extraction of the aromatic hydrocarbons. There is recovered,from the solvent extraction zone, an extract stream containing aromatichydrocarbons and a major proportion of the water-soluble solvent (morethan 99.0% by weight), and a raffinate stream containing non-aromatichydrocarbons and a relatively minor proportion (less than about 1.0%) ofthe water-soluble solvent. The raffinate stream is generally contacted,in countercurrent flow, with water to recover the solvent and to providea hydrocarbon concentrate substantially free from solvent. The extractstream is countercurrently contacted with steam in a solvent strippingzone, to remove the water-soluble solvent and to recover an aromatichydrocarbon concentrate. As hereinbefore set forth, the presentinvention encompasses a method of further reducing the solventconcentration of the aromatic concentrate.

The aromatic hydrocarbon concentration is generally withdrawn, as aprincipally vaporous phase, from an intermediate portion of the solventstripping zone. As such, it contains considerable quantities of steamand solvent, as well as entrained liquid (principally solvent). Thisaromatic concentrate is introduced into an entrainment separator for theremoval of the greater proportion of the entrained liquid phase, rich insolvent, therefrom. The entrainment separation zone may be mechanicallyarranged within the solvent stripping column, or take the form of aseparate vessel externally. The separated entrained liquid phase isreturned to the solvent stripping zone; the balance of the extract phaseis condensed and introduced, through a zone of turbulence, into anextract receiver for separation into an aromatic-rich product stream anda water concentrate.

Prior art solvent extraction processes have not recognized that a mixedvapor, such as one containing hydrocarbons and water, which is condensedinto two liquid phases, in a conventional condensing system, is not inequilibrium. This concept is extremely important when a third componentsuch as a solvent is present, especially when such solvent is completelymiscible in the water phase and at least partially miscible in thehydrocarbon phase. This very situation occurs in a solvent strippingzone from which hydrocarbon vapors, water vapors, solvent vapors andsome entrained liquid containing all three materials is removed,condensed and phase-separated. It is not unusual to observe that thehydrocarbon phase contains significantly more solvent, up to about 100times, than would reasonably be predicted from liquid/liquid equilibriumdata.

In accordance with the present invention, the aromatic concentrate ofreduced solvent content, but containing steam, is passed through a zoneof induced turbulence, at a condensed temperature of 60F. to about180F., and introduced into a second separation zone, for the separationof the liquid phases therein. There results a water stream containingsolvent and a third aromatic concentrate which is now substantially freefrom the solvent employed within the process; that is, the aromaticproduct contains less than 500 ppm. of solvent. The zone of turbulencemay be a pump, venturi, orifice, spray nozzle, or combinations thereof,etc., and serves to provide the intimate mixing which is lacking in theinitial condensing and phase separation. Liquid/liquid equilibrium will,therefore, be approached and the amount of solvent contained in theultimate aromatic product is greatly reduced. Up to a -fold reduction insolvent content can be reasonably expected.

The foregoing described technique is readily and advantageouslyintegrated into a present-day solvent extraction process. Thus, a mixedhydrocarbon charge stock containing about 70.0% by volume of aromatichydrocarbons and about 30.0% by volume of nonaromatic hydrocarbons, isintroduced into a solvent extraction zone wherein it counter-currentlycontacts a water-soluble, solvent, such as a polyethylene glycol. Asolvent-rich first extract phase is withdrawn from a lower portion ofthe extraction zone, and a solvent-lean first raffmate phase iswithdrawn from an upper portion of the solvent extraction zone. Thefirst raffinate stream, containing a minor proportion of both thewater-soluble solvent (about l.0% to about 5.0%, by weight) and aromatichydrocarbons, is introduced into a lower portion of a water-wash columnwherein it is contacted, countercurrently, with a first water stream.This water-wash step provides a second raffinate stream which issubstantially free from water-soluble solvent (less than about 0.05% byweight), and contains only a minor proportion of aromatic hydrocarbons(less than about 2.0%). The first water stream contains solvent and someentrained aromatic hydrocarbons. A second water stream, containingsolvent and non-aromatic hydrocarbons is withdrawn from a lower portionof the water-wash zone. admixed with a substantially pure (at leastabout 95.0% first aromaticrich stream, the mixture being introduced intoa separation zone. Separation is effected to provide a second aromaticstream containing non'aromatic hydrocarbons and a third water streamcontaining solvent and a minor quantity of aromatic hydrocarbons, butbeing substantially free from non-aromatic hydrocarbons. It is thisthird water stream which is utilized to generate the steam employed inthe solvent stripping zone to remove solvent from the solvent-rich firstextract phase recovered in the initial solvent extraction zone.

As in prior art processes, some of which have been previously described,the solvent recovered from the lower portion of the solvent strippingzone is recycled, at least in part, within the process to the solventextraction zone. The overhead stream from the solvent stripping zone,principally comprising hydrocarbons, steam and solvent vapors, ispreferably admixed with the aforesaid second aromatic stream, themixture being introduced into a so-called stripper overhead receiver.The substantially solvent-free aromatic-rich second extract phase iswithdrawn from a central portion of the solvent stripping zone, and ispassed into an entrainment separator. The second extract phase isprincipally vaporous, at a temperature in the range of about F. to about350F., and contains entrained liquid which is primarily solvent.Following a condensation technique, at a temperature of 60F. to about180F., the extract phase, reduced in solvent content, is passed througha zone of turbulence and into the extract receiver. The latter providesthe aromatic-concentrate product, containing less than about 500 ppm. ofsolvent, and a fourth, solvent-containing water stream. In preferredembodiments, as hereinafter indicated in the description of theaccompanying drawing, at least a portion of the aromatic-rich productstream is utilized as the first aromatic stream in admixture with thesecond water stream. Also, the fourth water stream is recycled, at leastin part, within the process as the first water stream introduced intothe water-wash zone.

A light hydrocarbon-containing stream is withdrawn from the stripperreceiver and utilized as backwash in a lower portion of the initialsolvent extraction zone. Also withdrawn from the stripper overheadreceiver is a fifth water stream containing some solvent and a minorproportion of hydrocarbons. In a preferred embodiment, this fifth waterstream is admixed with the aforesaid second water stream and firstaromatic stream, the mixture being introduced into the separation zone.

Principal among the multitude of advantages attendant the foregoingdescribed technique is the recovery of aromatic hydrocarbons ofexceptionally high purity, and particularly substantially free from theselected organic solvent. A corollary advantage involves theintroduction of a lesser quantity of non-aromatics into the solventstripping zone and, therefore, the aromatic purity is further increased.The overall process enjoys a simplified flow scheme resulting in lowercapital investment and subsequent operating costs.

SOLVENTS AND OPERATING CONDITIONS Generally accepted solvents, havingsolubility selectivity for aromatic hydrocarbons, are water-soluble,oxygen-containing organic compounds. Thus, one particularly preferredcategory of suitable solvents are those containing, in general, at leastone molar substituent selected from such radicals as hydroxyl, amino,cyano, carboxyl or nitro radicals. In order to be effective in a systemof extraction, such as the process provided by the present invention,the solvent component having the polar radical must have a boiling pointsubstantially greater than the boiling point of water, added to thesolvent composition for enhancing its selectivity; in general, thesolvent must also have a boiling point substantially greater than theend boiling point of the hydrocarbon feed stock. In most instances, thesolvent composition has a greater density than the hydrocarbon feedstock and is accordingly introduced into the uppermost portion of thesolvent extraction zone, thereafter flowing downwardly, countercurrentto the rising hydrocarbon feed stock introduced into the extraction zoneat about its mid-point.

Organic compounds suitable as the solvent may be selected from therelatively large group of compounds characterized generally asoxygen-containing compounds, particularly the aliphatic and cyclicalcohols, the glycols and glycol ethers, as well as the glycol estersand glycol ether-esters. The monoand polyalkylene glycols in which thealkylene group contains from 2 to 4 carbon atoms, such as ethyleneglycol, diethylene glycol, triethylene glycol and tetraethylene glycol,propylene glycol, dipropylene glycol, and tripropylene glycol, as wellas the methyl, ethyl, propyl and butyl ethers, and the acetic acidesters thereof, constitute a particularly preferred class of organicsolvents useful in admixture with water as the solvent composition ofthe present process. Various phenols such as phenol and resorcinol andtheir alkyl ethers, such as para-cresol, etc., are also effectivesolvents for aromatic hydrocarbons. Certain aliphatic nitriles,cyano-substituted ethers and amines, such as acetonitrile, and thediethers and polyalkylene polyamines constitute another group of usefulsolvents.

Another particularly suitable class of selective solvents are thosecommonly referred to as the sulfolanetype. By this, I intend a solventhaving a 5-membered ring, one atom of which is sulfur, the other fourbeing carbon, and having two oxygen atoms bonded to the sulfur atom.Many of these solvents may be illustrated by the following structuralformula:

wherein R,, R R and R are independently selected from the groupconsisting of a hydrogen atom, an alkyl group having up to 10 carbonatoms, an alkoxy radical having up to 8 carbon atoms and an arylalkylradical having up to 12 carbon atoms. Other solvents preferably includedare the sulfolenes such as 2-sulfolene or 3-sulfolene which have thefollowing structure:

The sulfolane solvents may be made by condensing a conjugated diolefinwith sulfur dioxide and then subjecting the resulting product tohydrogenation, alkylation, hydration and/or other substitution oraddition reactions. Other solvents which have high selectivity forseparating aromatics from non-aromatic hydrocarbons areZ-methylsulfolane, 2,4-dimethylsulfolane, methyl 2-sulfonyl ether,n-aryl-3-sulfonyl amine, 2-sulfonyl acetate.

The aromatic selectivity of the selected solvents is further enhanced bythe addition of water. Preferably, the solvents contain a small amountof water dissolved therein to increase the selectivity of the overallsolvent phase for aromatic hydrocarbons over non-aromatic hydrocarbons,without reducing substantially the solubility of the solvent phase foraromatic hydrocarbons. The presence of water in the solvent compositionprovides a relatively volatile material which is distilled from the fatsolvent in the extractive stripper to vaporize the last traces ofnon-aromatic hydrocarbon from the fat solvent stream by steamdistillation. The solvent composition contains from about 0.5% to about25.0% by weight of water, and preferably from about 3.0% to about 15.0%depending on the particular solvent utilized and the process conditionsunder which the extractor and solvent stripper are operated. By theinclusion of water in the solvent composition, the solubility ofaromatic hydrocarbons in the solvent, although somewhat reduced incomparison with a non-aqueous solvent, greatly decreases the solubilityof raffinate components in the solvent and also reduces the solubilityof solvent in the raffinate stream. Solubility of solvent in theraffinate, however, cannot be completely eliminated and, consequently,the raffinate stream inherently contains more or less solvent, dependingupon the proportion of water in the solvent composition. Although thequantity of solvent in the raffinate at any instant is relatively small,the cumulative effect of such small amounts of solvent in a streamremoved from the process flow and thus otherwise lost, greatly reducesthe efficiency and economy of the solvent extraction process. Recoverycan be accomplished efficiently by countercurrently washing theraffinate with water in a separate washing zone from which an aqueouswash effluent is recovered containing the solvent.

The solvent extraction zone is operated at elevated temperature and at asufficiently elevated pressure to maintain the feed stock, solvent andbackwash streams in the liquid phase. Suitable temperatures are withinthe range of from 80F. to about 400F. and preferably at an intermediatelevel from about 175F to about 300F. Suitable pressures are within therange of about atmospheric pressure up to about 400 psig. and preferablyfrom about 50 psig. to about 150 psig. Generally, the volume of backwashintroduced into the lower point in the extractor is at least 10% byvolume of the extract phase leaving the extractor. The solvent tohydrocarbon feed volumetric ratio is in the range of 1.0110 to about15.0110, and preferably from about 20:10 to about l0.0:l.0.

The solvent stripper is operated at moderate pressures and sufficientlyhigh reboiler temperatures to drive all the backwash non-aromaticcomponents and some of the aromatics, water and solvent overhead.Typical stripper pressures are from atmospheric to about I psig.,although the top of the stripper is generally maintained at from aboutpsig. up to about psig. The reboiler temperature is dependent upon thecomposition of the feed stock and the solvent. Generally, stripperbottom temperatures of from 275F. to about 360F. are satisfactory.

Other operating conditions will be given in conjunction with thedescription of one embodiment of the present invention as illustrated inthe accompanying drawing. Miscellaneous appurtenances, not believedrequired, by those possessing the requisite expertise in the appropriateart, for a clear understanding of the present method, have beeneliminated from the drawing. The use of details such as pumps,compressors, controls and instrumentation, heat-recovery circuits,valving, start-up lines and similar hardware, etc., is well within thepurview of one skilled in the art. It is understood that theillustration does not limit my invention beyond the scope and spirit ofthe appended claims.

DESCRIPTION OF DRAWING The accompanying drawing is presented for thepurpose of illustrating the method of integrating the present inventiveconcept into a solvent extraction process designed to separate andrecover aromatic hydrocarbons from a mixture thereof with non-aromatichydrocarbons. Miscellaneous appurtenances, not believed to be requiredfor a clear understanding of the technique involved, has been eliminatedfrom the drawing, or reduced in number.

With reference now to the drawing, the fresh feed charge stock, forexample a C plus fraction separated from the effluent of a naphthacatalytic reforming unit. is introduced via line I into solventextraction zone 2 at a locus above the mid-point thereof. The chargestock contains about 41.0% by weight of paraffins, 4.0% naphthenes and55.0% aromatic hydrocarbons. A solvent-rich stream is introduced intoextraction zone 2 by way of line 3 in an amount such that the solvent tohydrocarbon feed volumetric ratio is about 5.25:1.0; the solvent streamcontains about 6.0% by weight of water. A light hydrocarbon backwashphase, from line 4, is introduced into a lower portion of the extractionzone and serves to strip the heavier non-aromatic hydrocarbons from thesolvent-rich first extract stream withdrawn by way of line 5.

A first raffinate stream containing some aromatic hydrocarbons (about2.3%) and solvent (about 2.1%) is withdrawn by way ofline 6 andintroduced thereby into a lower portion of water-wash column 7. A firstwater stream, containing a minor amount of both solvent, about 3.0% byweight, and aromatic hydrocarbons, less than about 0.1%, andsubstantially free from nonaromatic hydrocarbons (less than about0.01%), is introduced into an upper portion of water-wash column 7 byway ofline 8. A second raffinate phase, containing less than 300 ppm. byweight of solvent, is removed from the process by way of line 9. Asecond water stream, containing the solvent in the first water streamand that removed from the first raffinate stream, and both dissolved andentrained non-aromatic hydrocarbons, is withdrawn by way ofline l0 andintroduced via line 11 into separation zone I2.

Also introduced into separation zone 12, in admixture with the secondwater stream in line 10, is a substantially pure first aromatichydrocarbon from line 31, the source of which is hereinafter set forth.A second water stream, containing at least 90.0% of the nonaromatichydrocarbons in the second water stream. is withdrawn from an upperportion of separation zone 12 by way of line 13, while a third waterstream substantially free from nonaromatic hydrocarbons is withdrawn byway of line 14.

The third water stream is utilized to generate steam in steam generator15, employing the solvent-rich first extract stream in line 5 as theheat-exchange medium. The cooled extract stream is introduced by way ofline 17 into solvent stripping zone 18 wherein it countercurrentlycontacts the generated stream being introduced by way of line 16. Asolvent concentrate is removed by way of line 3 and recycledtherethrough to the upper portion of solvent extraction zone 2. Aprincipally vaporous phase, containing steam, hydrocarbons and solventis withdrawn by way of line 19, admixed with the second aromatic streamin line 13, and introduced into stripper receiver 20.

A second extract stream, of reduced solvent content (about 2.7% byweight), concentrated in aromatic hydrocarbons and containing steam, iswithdrawn from an intermediate portion of solvent stripper 18 by way ofline 21. The second extract stream, at a temperature of 220F.,containing entrained liquid, is introduced into separator 22, from whichentrained solvent is withdrawn by way of line 23 for re-introductionthereby into solvent stripper 18. A third extract stream, containingabout 0.5% solvent, is introduced through line 24 into condenser 25,wherein the temperature is decreased to a level of about F. Thecondensed third extract stream is passed via line 26 through a zone ofturbulence, shown in this illustration as motor driven mixer 27. Theturbulent stream flows through line 28 into extract receiver 29, fromwhich a fourth water stream, containing substantially all the solvent inthe third extract stream, is removed by way of line 8 and preferablyrecycled, at least in part, as the first water stream-introduced intowater-wash column 7. The substantially pure aromatic concentrate iswithdrawn through line 30..In a preferred embodiment, at least a portionis diverted through line 31 to serve as the substantially pure firstaromatic stream combined with the second water stream in line 10.

Stripper receiver 20 serves to provide a light hydrocarbon backwashstream in line 4 which is introduced into the lower portion ofextraction zone 2 as hereinbefore set forth. In a preferred embodiment,a fifth water stream is withdrawn by way of line 11, admixed with thesecond water stream in line and the first aromatic stream in line 14,the mixture continuing through line ll into separation zone 12.

The foregoing indicates the method by which the present invention isutilized to separate and recover an aromatic concentrate substantiallyfree from both solvent and non-aromatic hydrocarbons. The productaromatic stream contains about 500 ppm. of solvent, whereas prior artprocesses absent the zone of turbulence of the present invention,contain about 2,000 ppm. of solvent.

1 claim as my invention:

1. In a process for the solvent extraction of polar hydrocarbons from amixture thereof with non-polar hydrocarbons, the method of recoveringsaid polar hydrocarbons, substantially free from solvent, whichcomprises the steps of:

a. contacting said mixture in a solvent extraction zone with awater-soluble solvent selective for the adsorption of polar hydrocarbonsto form a polar hydrocarbon-rich solvent stream and a solvent-leanraffinate stream;

b. contacting said polar hydrocarbomrich solvent stream from the solventextraction zone with steam to provide (i) a first solvent concentratesubstantially free from polar hydrocarbons, (ii) a vaporous streamcontaining steam, solvent and hydrocarbons and (iii) a vaporous firstpolar hydrocarbon concentrate of reduced solvent content, and containingsteam;

c. separating said first polar hydrocarbon concentrate, in a firstseparation zone, to provide (i) a second solvent-rich stream and (ii) avaporous second polar hydrocarbon concentrate of reduced solventcontent, and containing steam;

d. passing said second polar hydrocarbon concentrate through a zone ofturbulence at a temperature of about 60F. to about l80F.; and,

e. separating the resulting turbulent polar hydrocarbon concentrate, ina second separation zone, to provide (i) a water concentrate, containingsolvent, and (ii) a third polar hydrocarbon concentrate substantiallyfree from solvent.

2. The method of claim 1 further characterized in that said solvent is apolyalkylene glycol.

3. The method of claim 1 further characterized in that said solvent is asulfolane-type organic compound.

4. The method of claim 1 further characterized in that said polarhydrocarbons are aromatic.

5. The method of claim 1 further characterized in that said non-polarhydrocarbons are naphthenes.

6. The method of claim 1 further characterized in that said zone ofturbulence comprises a pump.

7. The method of claim 1 further characterized. in that said zone ofturbulence comprises a venturi.

8. The method of claim 1 further characterized in that said zone ofturbulence comprises an orifice.

9. In a process for the solvent extraction of aromatic hydrocarbons froma mixture thereof with non-.

aromatic hydrocarbons, the method of recovering said aromatichydrocarbons, substantially free from nonaromatic hydrocarbons andsolvent, which comprises the steps of:

a. contacting said mixture with a water-soluble solvent, selective forthe adsorption of aromatic hydrocarbons, in a solvent extraction zone,to provide (i) a solvent-rich first extract stream, and (ii) asolvent-lean first raffinate stream;

b. contacting said first raffinate stream with a first water stream toprovide (i) a second raffinate stream substantially free from solventand concentrated in non-aromatic hydrocarbons, and (ii) a second waterstream containing solvent and a minor quantity of hydrocarbons;

c. admixing said second water stream with a substantially pure, firstaromatic stream and separating the resulting mixture to provide (i) asecond aromatic stream, containing non-aromatic hydrocarbons, and (ii) athird water stream substantially free from non-aromatic hydrocarbons;

d. generating steam from said third water stream and contacting saidfirst extract stream from said solvent extraction zone therewith in asolvent stripping zone;

e. recovering, from said stripping zone,,(i) a vaporous streamcontaining steam, hydrocarbons and solvent, (ii) a first solvent-richstream, and (iii) a vaporous second extract stream, concentrated inaromatic hydrocarbons and containing solvent and steam;

f. separating said second extract stream, in a first sep aration zone,to provide (i) a second solvent-rich stream, and (ii) a third extractstream of reduced solvent content and containing steam;

g. passing said third extract stream through a zone of turbulence at atemperature in the range of 60F. to about lF.; and,

h. separating the resulting turbulent third extract stream, in a secondseparation zone to provide a fourth water concentrate containingsolvent, and to recover aromatic hydrocarbons substantially free fromsolvent.

10. The process of claim 9 further characterized in that said firstraffinate stream is contacted with at least a portion of said fourthwater concentrate as said first water stream.

11. The process of claim 9 further characterized in that said secondwater stream is admixed with at least a portion of said aromatichydrocarbons as said sub stantially pure first aromatic stream.

1. IN A PROCESS FOR THE SOLVENT EXTRACTION OF POLAR HYDROCARBONS FROM AMIXTURE THEREOF WITH NON-POLAR HYDROCARBONS, THE METHOD OF RECOVERINGSAID POLAR HYDROCARBONS, SUBSTANTIALLY FREE FROM SOLVENT, WHICHCOMPRISES THE STEPS OF: A. CONTACTING SAID MIXTURE IN A SOLVENTEXTRACTION ZONE WITH A WATER-SOLUBLE SOLVENT SELECTIVE FOR THEADSORPTION OF POLAR HYDROCARBONS TO FORM A POLAR HYDROCARBON-RICHSOLVENT STREAM AND A SOLVENT-LEAN RAFFINATE STREAM; B. CONTACTING SAIDPOLAR HYDROCARBON-RICH SOLVENT STREAM FROM THE SOLVENT EXTRACTING ZONEWITH STEAM TO PROVIDE (I) A FIRST SOLVENT CONCENTRATE SUBSTANTIALLY FREEFROM POLAR HYDROCARBONS, (II) A VAPOROUS STREAM CONTAINING STEAM,SOLVENT AND HYDROCARBONS AND (III) A VAPOROUS FIRST POLAR HYDROCARBONCONCENTRATE OF REDUCED SOLVENT CONTENT, AND CONTAINING STEAM; C.SEPARATING SAID FIRST POLAR HYDROCARBON CONCENTRATE, IN A FIRSTSEPARATION ZONE, TO PROVIDE (I) A SECOND SOLVENT-RICH STREAM AND (II) AVAPOROUS SECOND POLAR HYDROCARBON CONCENTRATE OF REDUCED SOLVENTCONTENT, AND CONTAINING STEAM; D. PASSING SAID SECOND POLAR HYDROCARBONCONCENTRATE THROUGH A ZONE OF TURBULENCE AT A TEMPERATURE OF ABOUT 60*F.TO ABOUT 180*F.; AND, E. SEPARATING THE RESULTING TURBULENT POLARHYDROCARBON CONCENTRATE, IN A SECOND SEPARATION ZONE, TO PROVIDE (I) AWATER CONCENTRATE, CONTAINING SOLVENT, AND (II) A THIRD POLARHYDROCARBON CONCENTRATE SUBSTANTIALLY FREE FROM SOLVENT.
 2. The methodof claim 1 further characterized in that said solvent is a polyalkyleneglycol.
 3. The method of claim 1 further characterized in that saidsolvent is a sulfolane-type organic compound.
 4. The method of claim 1further characterized in that said polar hydrocarbons are aromatic. 5.The method of claim 1 further characterized in that said non-polarhydrocarbons are naphthenes.
 6. The method of claim 1 furthercharacterized in that said zone of turbulence comprises a pump.
 7. Themethod of claim 1 further characterized in that said zone of turbulencecomprises a venturi.
 8. The method of claim 1 further characterized inthat said zone of turbulence comprises an orifice.
 9. In a process forthe solvent extraction of aromatic hydrocarbons from a mixture thereofwith non-aromatic hydrocarbons, the method of recovering said aromatichydrocarbons, substantially free from non-aromatic hydrocarbons andsolvent, which comprises the steps of: a. contacting said mixture with awater-soluble solvent, selective for the adsorption of aromatichydrocarbons, in a solvent extraction zone, to provide (i) asolvent-rich first extract stream, and (ii) a solvent-lean firstraffinate stream; b. contacting said first raffinate stream with a firstwater stream to provide (i) a second raffinate stream substantially freefrom solvent and concentrated in non-aromatic hydrocarbons, and (ii) asecond water stream containing solvent and a minor quantity ofhydrocarbons; c. admixing said second water stream with a substantiallypure, first aromatic stream and separating the resulting mixture toprovide (i) a second aromatic stream, containing non-aromatichydrocarbons, and (ii) a third water stream substantially free fromnon-aromatic hydrocarbons; d. generating steam from said third waterstream and contacting said first extract stream from said solventextraction zone therewith in a solvent stripping zone; e. recovering,from said stripping zone, (i) a vaporous stream containing steam,hydrocarbons and solvent, (ii) a first solvent-rich stream, and (iii) avaporous second extract stream, concentrated in aromatic hydrocarbonsand containing solvent and steam; f. separating said second extractstream, in a first separation zone, to Provide (i) a second solvent-richstream, and (ii) a third extract stream of reduced solvent content andcontaining steam; g. passing said third extract stream through a zone ofturbulence at a temperature in the range of 60*F. to about 180*F.; and,h. separating the resulting turbulent third extract stream, in a secondseparation zone to provide a fourth water concentrate containingsolvent, and to recover aromatic hydrocarbons substantially free fromsolvent.
 10. The process of claim 9 further characterized in that saidfirst raffinate stream is contacted with at least a portion of saidfourth water concentrate as said first water stream.
 11. The process ofclaim 9 further characterized in that said second water stream isadmixed with at least a portion of said aromatic hydrocarbons as saidsubstantially pure first aromatic stream.